The present invention relates to generating waveforms. In particular, the invention relates to a transmit and receive circuit for an ultrasound system.
Short, high-energy transmit waveforms drive ultrasound transducers for diagnostic medical imaging. The transmit waveforms are generated by switching pulsers. Simple switching pulsers avoid dissipation associated with linear output amplifiers, but provide limited control of the transmit energy spectrum. For example, simple bipolar or unipolar waveforms are generated.
U.S. Pat. Nos. 6,083,164 and 6,050,945 disclose transmit and receive circuitry using switching pulsers. FIG. 14 of U.S. Pat. No. 6,083,164 discloses two switches S1, S2 connected to primary windings with a voltage source. The secondary winding of the transformer achieves a positive or negative voltage value for generating a bipolar waveform at the transducer element. With an extra primary winding, associated switches and different source voltage, different amplitude bipolar waveforms may be generated by the transformer. Since different voltages are used for each of the primary windings, bipolar waveforms with two different amplitudes may be generated. The flux path in the transformer is common to all of the windings, so bipolar waveforms responsive to only one of the two voltages are generated for any particular transmit pulse. A current biased diode bridge bypasses the transformer for reception of echo information.
More complex transmit waveforms with controlled energy spectrums are generated with the transmit beam former of U.S. Pat. No. 5,675,554. A digital to analog converter generates a complex multilevel waveform, such as a multiple cycle sinusoidal waveform with a Gaussian envelope. An amplifier is provided after the digital to analog converter. A linear amplifier with high-powered dissipation is used to preserve the desired high-power waveform.